Conventionally, pure-tungsten contacts have been predominantly used as electrical contacts for automobile distributors or for magnetos of autocycles.
Tungsten is used in such severe operating conditions for its favorable characteristics such as high melting point, high hardness, and high arc resistance.
The tungsten contacts are generally produced by the powder metallurgy since the metallurgy is hardly applicable to the production of tungsten contacts which has high melting point.
However, the powder metallurgy necessitates the swaging after the sintering to produce tungsten contacts of high density and such swaging requires a good deal of processing time. Thereby tungsten contacts produced by such method have been extremely expensive.
Furthermore, in a very humid atmosphere, tungsten readily forms an oxide on the surface thereof which increases the contact resistance and eventually impairs the conductivity of the contacts.
One method has been developed for overcoming the defects of the above production method so as to obtain a contact material of improved properties.
The method is based on a finding that the addition of nickel and cobalt to tungsten can provide the activated sintering. Although the method has succeeded in producing of a contact material of high oxidation resistance and also has succeeded in shortening the time necessary for the completion of the overall process, the material produced by the above method has shown poor mechanical properties. For example, when the contacts made of such material receive an impact caused by riveting or a distortion caused by brazing, the contacts readily give rise to cracks therein.
Accordingly, such contacts are rarely produced nowadays.
Accordingly, it is an object of the present invention to provide electrical contact material which can resolve the aforementioned defects of conventional contact material including pure tungsten.
It is another object of the present invention to provide electrical contact material which can be manufactured in an inexpensive manner.
It is still another object of the present invention to provide electrical contact material which has a favorable resistance to the oxidation.
It is further an object of the present invention to provide electrical contact material which has favorable mechanical properties.